Use of of as a hypergolic additive for liquid oxygen



Feb. 23, 1965 A. D. KIRSHENBAUM ETAL 3,170,282.

USE OF 0 1 AS A HYPERGOLIC ADDITIVE FOR LIQUID OXYGEN Filed Jan. 29, 1963 SOLUBILITY 0F 0 F IN LIQUID OXYGEN.

(GRAMS 0 F 100 GRAMS LIQ. 0

8.2 LIQ. N2)

Abraham. D. Kirshenboum Charles S. Stokes Aristid V. Grosse dd INVENTORS.

United States atent 3,170,282 USE OF F AS A HYPERGOLIC ADDETIVE FOR LIQUID OXYGEN Abraham D. Kirshenbaum, Philadelphia, Charles S.

Stokes, Willow Grove, and Aristid V. Grosse, Haverford, Pa., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Jan. 29, 1963, Ser. No. 254,846

6 Claims. (Cl. 60-314) engines. In particular, this invention pertains to an improvernent in the operation of bipropellant liquid rocket motors and liquid oxidizer compositions especially useful in the operation of such rocket motors.

The method of operating bipropellant liquid rocket motors is old in the art.; Generally, a bip-ropellant liquid rocket engine comprises a fuel-tank, and oxidizant tank, an injection system, a combustion chamber, and an exhaust nozzle. The fuel and om'dizer areffed from their respective tanks through the injector into the combustion zone Where they react to produce gases at high temperature and-pressure. These gases are ejected through the exhaust, thus, producing a thrust which propels the rocket. The actual thrust produced by such a motor is obviously dependent on many variables. Illustrative of these variables are the particular fuel and oxidizer, the ratio of fuel to oxidizer, and the rate at which the oxidant and fuel are fed to the'combustion chamber.

If the fuel and oxidizer are not hypergolic, then it is necessary to provide some means of igniting the propellants in the-combustion chamber. The necessity of having to incorporate a-means of ignition is undesirablesince another possible area of rocket failure is thereby 1ntro-- duced. Moreover, when the fueland oxidizer ignite spontaneously on contact, there is less possibility of an excess of fuel and oxidizer accumulating in the combustion chamber prior to ignition. Too. large.,a excess of fuel the oxdizers. -Among the fuels which are hypergoliewith 1 45 these oxidizers are mixtures of mercaptans and alkenyl monoarriines such as tertiary-butyl mercaptan, dienes such as Z-mthyl-l, 3-butadiene, acetylenic compounds such as 1o This. inventionrelates to a method of operating rocket 3,179,282 Patented Feb. 23, 1965 previously mentioned hereinabove, it is now possible to proparkyl' alcohol, and ethylene imine Howeventhe's'e';

fuels are relatively costly in comparison-tothe cheaper hydrocarbon fuels when the large volumes necessary for use in rockets are considered. Moreover, the acid oxidizers createmany additional problems; in handling, -storage, and. use because. of. their ltoxicit'y and corrosivechar acteristics.-.1

. One answer to the above prdblem isthe useofiliquid.

oxygen as the oxidizer andgthe" inexpensive hydrocarbon;

fuels such as gasoline. Theliquid oxygen is non-toxic" and non-corro ssive in addition to being superior-as an oxidizer. Furthermore, the hydrocarbon fuels are easily handled andstoredJfAnother fuel also being studied for- 7 use with liquid oxygen is liquidvhydrogen The-liquid hydrogen-liquid oxygen bipropellant system can theoretically develop a specific impulse in excess of 340 seconds.

A hinderance in the bipropellant systems using liquid oixygehi isthe.lackof'practicalhypergolie fuels. While sudden pressurization-may cause mixtures of liquid oxyadd the advantage ofspontaneous ignition. This ad vantage precludes the necessity of an ignition means inthe rocket motor or may be used as a safety factor in conjunction with other ignition means. This is of particular usefulness when it is desired to cease combustion and reignite the propellants during flight of the rocket.

In accordance with the foregoing, it is an'object of the invention to set forth a composition of matter comprising trioxygen difiuoride dissolved in liquid oxygen.

it. is a further object of this invention to describe a means of improving the method of operating bipropellant liquid rocket engines which'employ liquid oxygen as an oxidizer by substituting therefor a solution of trioxygen difiuoride in liquid oxygen. a

It is a still further object of this invention to describe a method of operating a bipro'pellant liquid rocketengine employing a solution of trioxygen difluoride in liquid; oxygen and a fuel hypergolic therewith. a

Another object of the invention is to stabilize combustion of the fuel in the combustion chamber of bipropellant liquid rocket motors employing liquid oxygen by. adding trioxygen difluoride to theliquid oxygen.

These and other objects will become apparent from the detailed description of the invention presentedhereinbelow. 7 a .1 f

The graph illustrates the solubility of trio xygenkdi fluoride in-liquid oxygen at .various temperatures Trioxygen.ditluoride, or ozone fiuoride as it is some? The pure compound can be evaporated rapidly, refluxed] or thermally decomposediwithout explosion. However,

1 in cont'act with oxidizable-matter, combustion or explosion may occur. At the. boiling point of liquidnitrog' en (77 K'.), decompositionlof trioxygen difluoride is negligible and'it may be store d'for extended periods as a solid at this temperature.- At'the.boiling point of oxygen, it decomposesat the'rate ofabout4% each 24 hours. Tri-. oxygen difluoride is safer and easier to handle than 'e'ither',

' ozone on-fluorine since ozone is shock sensitiy'e an fiuorine'is highly corrosive. An electric spark 'intrioxygen difluoride or-"solutions of trioxygen difiuoride in liquid? oxygen causes only smooth, slowdecomposition, due to [thermal energy. v I

.Thesolutions of trioxygen difiuoride in liquid oxygen: are made by thoroughly mixing "the, two ,components. Trioxygen" difiuoride can be employed in an amount up to the quantity necessary to achieve a satur'ated solution. 5 Theseamounts can be determined from the gr'aphf For below in Table 1.

example, at 90 K., the boiling point of oxygen, 0.11 gram of trioxygen difiuoride will dissolve in each 100 milliliters of liquid oxygen; at 77 K., 0.046 grams will dissolve per 100 milliliters of liquid oxygen.

It is apparent that the temperatures of the solution during preparation and storage should preferably be maintained slightly below the boiling point of liquid oxygen to reduce loss of oxygen. Liquid nitrogen and/or liquid oxygen baths for the mixing apparatus can be employed to facilitate temperature control.

Glassware, such as Pyrex glassware, can be used as containers for storage and mixing. The solutions are best stored under an inert atmosphere such as helium. This is a safety measure to prevent contact with oxidizable materials. Moreover, the solutions are conveniently pumped under by means of helium pressure.

As would be expected from the solubility of trioxygen difluoride as shown in the graph, cooling a saturated solution, from 90 K. to 77 K. for example, results in the precipitation of the excess trioxygen difluoride. Likewise, oxygen boil-off of a saturated solution results in some trioxygen difluoride coming out of solution. For this reason, it is advisable to employ solutions containing less than the saturation quantity of trioxygen difiuoride.

In practical application, the liquid oxygen-trioxygen difluoride solutions will be at the boiling point of liquid oxygen (90 K.) when in the liquid oxygen tanks of the rockets, since it is usually impractical to maintain a temperature less than this. It has been found that a solution of 0.05% by weight trioxygen difiuoride in liquid oxygen will ignite spontaneously when brought in contact with most rocket fuels including amines, hydrocarbons, alkanols, and hydrogen. At this concentration, 50% of the liquid oxygen can boil from the solution at 90 K. without any precipitation of trioxygen difluoride. Furthermore, as the boil-off concentrates the solution, the percent by weight trioxygen difluoride increases. Thus, there is no loss in the ability to spontaneously ignite in contact with fuels. In fact, this ability is increased With the increase in the percent by weight trioxygen difluoride.

One particularly beneficial characteristic of the solutions of 0.05% by Weight trioxygen difluoride in liquid oxygen is the density. The density difference between liquid oxygen andthe trioxygen difluoride-liquid oxygen solution is less than 0.03%. Therefore, littleif any design changes will be necessary in present rocket motors with the use of the solution of trioxygen difiuoride in lieu of liquid oxygen.

Initial studies'of the spontaneous ignition of various fuels were made by means of a series of open cup tests. Essentially this test comprised placing five cubic centimeters of the fuel to be tested in an aluminum cup. Then a few milliliters of 0.05% O F in liquid oxygen was added. The results of such 'a series of tests are given Table 1 [Open cup tests of 0.05% of O Fz ivith various fuels] Vol. of Vol. of Reaction Fuel fuel, ml. oxidilzcr, time, sec. Remarks ZIP- 4 s 5 3.4 Fire. JP-4 5 10 12. 4 Explosion. UDMH (Unsymmetri- 5 5 O Instantaneous cal lgimethyl Hydraignition. zine U-DETA* 5 1 Do. 50% (by vol.) UDMH 3 0.. Do.

in JP4. (by vol.) UDMH 5 3 0 Do.

in 5% (by vol.) UDMII 5 5 0 Do.

in .TP-4. 1% (by vol.) .UDMH 5 5 0 D0.

in JP-4. Y

60% by volume UDMH-50% by volume diethylenc triamine.

The fue.s listed in Table I are by no means all that are hypergolic with the trioxygen difluoride-liquid oxygen solutions of the invention. In fact, all fuels tested were found to be hypergolic. Any of the JP or RP type of fuels such as JP-3 and JP-4 function satisfactorily. Apparently any conventional fuel is hypergolic with the trioxygen difluoride-liquid oxygen solutions. Examples of suitable specific fuels are diethylene triamine, hydrazine, kerosene, furfuryl alcohol, aniline, orthotoluidine, trimethylamine, propargyl alcohol, ethanol, butanol, methylvinylpyridine, diethyl ether, propane, butane, and octane. It is obvious to those skilled in the art that, to be used successfully in a bipropellant rocket engine, the fuels should be liquids or gases. However, the trioxygen diilunride-liquid oxygen mixture is hypergolic with most solid combustible materials.

The results of the open cup tests clearly demonstrated that spontaneous ignition in a rocket motor is possible when a solution of trioxygen difluoride is employed. Nevertheless, to verify this conclusion and obtain more data as to the performance of the new hypergolic additive, additional tests were performed in small test motors. Typical results of these tests in 7.5 atmosphere microrocket motors using conventional fuels are tabulated below. Table II gives the results using a liquid oxygen oxidizer containing 0.10% by weight O F while Table II gives the results of tests utilizing 0.05% by weight 0 1 in liquid oxygen.

Table II [Ignition Tests 0.1 Wt. 03F; in LOX] Starting Pressure Fuel Injector* Remarks Fuel Oxidizer Ethyl alcohol 10 70 3 Fuel 011 1 Immediate igni- 100 0 Oxidizcr. tion. Propane (at 10 70 do Ignition outside 78 0.). chamber. JP-4 4 20 3 Fuel on 3 Immediate igni- Oxidizer. tion. U-DETA 4 20 d0 Do.

*All injectors were fuel cooled.

Table III [Ignition Tests of 0.05% 0 F; in LOX] Starting Pressure Fuel Injector* Remarks Fuel Oxidizer Ethyl alcohol 4 20 3 Fuel on 1 Instantaneous Oxidizer. ignition. 5P4 4 20 do Instanteous ignition in each of 3 runs. U-DETA 4 20 do D0. H2 (gas at 90 2O 1 Fuel on 1 Instantaneous K.) Oxidizer, ignition in both waterof 2 runs. cooled.

*Unless otherwise noted all injectors were fuel cooled.

- When the pressure on the fuel and oxidizer was again increased, the flame was blown out. The failure at high pressure was due to the inability to control the ratio of fuel to oxidizer in the combustion chamber since, in the micro-motor system, high pressure applied to the fuel and oxidizer could not be properly regulated so as to maintain the desired flow of fuel and oxidizer into the combustion chamber. In the operation of larger motors, fuel and oxidizer pressure is easily regulated thus providing correct flow of fuel and oxidizer into the combustion chamber and assuring hypergolic ignition.

The hydrogen test result given in Table III was obtained by cooling hydrogen gas in coiled coppertubing immersed in liquid nitrogen and then introducing the hydrogen into the combustion chamber. Under maximum flow conditions (.003 lb./sec.) their cooling systems maintained the gas at a temperature of from 85 K. to 90 K.

.To facilitate the achievement of dependable hypergolic ignition, the fuel and oxidizer should be injected into the combustion chamber in such a manner as to allow thorough mixing of the two while at the same time providing maximum evaporation of oxygen from the liquid oxygentrioxygen difluoride solutions. This results'in the concentration of trioxygen difluoride and, thus, as previously explained hereinabove, assists hypergolic ignition. In view of this, the injector employed with the liquid oxygen-trioxygen difluoride solution can be of considerable assistance in achieving spontaneous ignition. Typical specifications of injectors employed in some of the micro-motor tests are given in Table IV below.

Nevertheless, injector design can be varied considerably as the particular motor may require. A two-port injector having an impingement angle of 90 allowed hyPergolic ignition of JP-4 and liquid oxygen containing 0.05% by weight trioxygen difluoride.

In addition to providing hypergolic' ignition, the solution of trioxygen difluoride in liquid oxygen provides irnproved combustion stability over the fuel and liquid oxygen-alone. This was evidenced not only from visual observationand highspeedphotography, but also from the'combustion chamber pressures traces.

No significant difierences in specific impulse values were obtained experimentally between the liquid oxygontrioxygen difluoride solutions and pure liquid oxygen.

However, it is expected that a slight, insignificant increase in specific impulse occurs.

Iu-order to investigate the handling characteristics of the trioxygen difluoride-liquid oxygen solutions, open-cup compatibility tests were made with those engineering maevaporate completely, thus exposing the material to the original solution as'well as dinitrogen difi'uoride and finallyfiuorine vaporfor short times as the solution war-med Table V [Open cup compatibility tests of engineering materials with 0.05% 0 F; in liquid oxygen} 1 Glass Material Remarks B Metal Staii z iless steel, No. 303-- No sappreciablejreaetion Stainless steel, No. 316 Do. Stainless steel, No. 321.- Do. Stainless steel, No. 347 Do. Aluminum Do. Copper Do. Brass No appreciable reaction;

surface pitted on continned exposure. Stzanlless steel carpenter No' appreciable reaction.

0 Titanium alloy beta- Do.

120-VCA Magnesiumllthium Do.

(14.1%) alloy Magnesium-thorium Do.

alloy XK31. Packing gasket. Kel-F elastomer Delayed (50 sec.) slight (plasticized) reaction. Allpax 500 No appreciable reaction. Allpax 500 (fluorolube Do.

T-80 treated). Teflon Do. I M 76 Do Duroid 3400 Do Lo- Do. Polyethylene film Dieilayed sec.) ignion. Librileaizts and Fluorolube T-80 (T-45) No appreciable reaction.

ea an s.

Halocarbon, series 11-14. Delayed (50 sec.) slight reaction. K2152]? oil, alkane No. Do. Molykote Z No appreciable reaction. Oxylube 70? No appreciable reactions AR-lF, LOX lube Delayed (50 sec.) slight reaction.

= No appreciable reaction indicates no fire, flame, or other The results of the above mentioned test as seen from Table V showed that with the possible exception of some chlorotrifluoroethylene base materials (Halocarbon No.

1l-15, Kel-F elastomer, KelF alkone No. 464 oil), the trioxygen difiuoride-liquid oxygen solutions do not react with the materials most frequently employed in space vehicle liquid oxygen propulsion systems.

' Thus, it is seen that trioxygen diiluoride not only offers the advantage of a hypergolic additive, it is compatible with rocket motor materials and stabilizes combustion within the motor. At the same time, .no loss in specific impulse is encountered. If anything, an increase in the J specific impulse, though negligible in'amount, is to be expected. The combination of advantages makes trioxygen difiuoride an especially suitable additive for liquid oxygen to be employed as an oxidizer in bipropellant liquid rocket systems.

The above detailed description isfor the purpose of illustration only and is in no way to be considered a limita tion of the invention. Many obvious modifications maybe applied to the invention without departing from the spirit and scope of the invention asdefined in the appended in" air. Such tests, while purely" qualitative, are very" severe. I

Since the test results could be aifected byfcondensed;

moisture coating theniaterials being studied, the tests" I were repeated taking care toiexclude moisture. The re-v 1 sults "were identical with the testresults where moisture? was not excluded. Table V. gives theresults of these'ltests."

claims. I q We claim:

1. In the operation of bipropellant liquid rocket engines which employ liquid oxygen as the oxidizer for the fuel, the improvement which comprises substituting for said liquid oxygen a solution of from about 0.05% to 0.10% by weight of trioxygen difiuoride in liquid oxygen.

--2.' The improvement according to claim 1, wherein a I solution of about 0.05% by weight of trioxygen difluoride 1n liquld oxygen is substituted for said liquid oxygen.

-3-. method for operating a bipropellant liquid react1on motor wh1ch comprises bringing togetherin a combust on zone of said motor a solution of about 0.05 to 0.10% by weight trioxygen difluoride in liquid oxygen and a fuel which is hypergolic with said solution.

4. The method according to claim 3, wherein the solution of liquid oxygen and trioxygen difiuoride is about 0.05 by weight trioxygen difluoride.

5. A method for operating a bipropellant liquid reaction motor which comprises bringing together in a combustion zone of said motor a solution of about 0.05% to about 0.10% by weight trioxygen difiuoride in liquid oxygen and a fuel selected from the group consisting of ethanol, propane, unsymmetrical dimethyl hydrazine, hydrogen, unsymmetrical dimethyl hydrazine-diethylene triamine mixture, and J P-4.

6. The method according to claim 5, wherein the solu- 8 tion of liquid oxygen and trioxygen difiuoride is about 0.05 by weight trioxygen difluoride.

References Cited by the Examiner UNITED STATES PATENTS 3/60 Kanarek 1491 CARL D. QUARFORTH, Primary Examiner. 

5. A METHOD FOR OPERATING A BIPROPELLANT LIQUID REACTION MOTOR WHICH COMPRISES BRINGING TOGETHER IN A COMBUSTION ZONE OF SAID MOTOR A SOLUTION OF ABOUT 0.05% TO ABOUT 0.10% BY WEIGHT TRIOXYGEN DIFLUORIDE IN LIQUID OXYGEN AND A FUEL SELECTED FROM THE GROUP CONSISTING OF ETHANOL, 